1. Field of the Invention
The invention relates to a method for determining a type of an optical disk and an optical storage device. More particularly, the invention relates to a method for determining a type of an optical disk based on a spherical aberration estimate and an optical storage device.
2. Description of Related Art
Optical storage devices available in the market are mainly categorized into two types, i.e., digital versatile disks (DVD) and compact disks (CD). The two types of disks are extensively applied, and accordingly manufacturers endeavor to research and manufacture optical storage devices capable of reading both types of disks. The optical storage devices capable of reading both types of disks are inevitably required to be able to determine the types of the disks.
At present, the types of disks can be determined based on a disk reflection rate because the disks are sensitive to specific light wavelength. Alternatively, the types of disks can be determined based on thickness of disk substrate. Specifically, the types of disks can be determined based on the disk reflection rate because dye on the data layer of CD has a relatively high reflection rate when reflecting the laser beam having a wavelength of 780 nm, while dye on the data layer of DVD has a relatively high reflection rate when reflecting the laser beam having a wavelength of 650 nm. However, the reflection rate is prone to be affected by different disks, thus causing erroneous determination of the types of disks. For instance, in case that the disk is scratched or the disk reflection rate is low, the system is unable to correctly compare the measured error signals (e.g., focus error signals), and thereby the types of disks are mistakenly determined.
The types of disks can also be determined based on the thickness of the disk substrate. This is mainly because the thickness of the CD substrate is 1.2 mm, while the thickness of the DVD substrate is 0.6 mm. By focusing the laser beam on a transparent layer of the disk to generate reflection signals, the types of disks can be determined based on the thickness of the disks when a slope of a focus driving signal remains constant. Nevertheless, if the reflection rate at the surface of the disk is overly small, the location of the surface of the disk may be mistakenly detected or cannot be detected. In addition, the slope of the focus control signal is often changed together with variations in manufacturing conditions of actuators or motor drivers. Hence, errors often occur when the time difference from the surface of the disk to the reflection layer is measured, such that the system cannot accurately determine the thickness of the disk.